Method of identifying workstations that performed work on a workpiece

ABSTRACT

A method of identifying workstations that performed work on a workpiece in a work line having a plurality of zones, wherein each zone includes workstations that perform the same type of operation. In accordance with the method, the workpiece is moved to and from workstations by a plurality of autoloaders. After the workpiece is worked on in a particular workstation, an autoloader moves the workpiece to a drop-off station where the workpiece is marked with a mark indicating that the workstation worked on the workpiece. When the workpiece is finished, the workpiece has a plurality of marks disposed in different locations of the workpiece. For each of the marks, the location of the mark in combination with the nature of the mark comprises a code that identifies a particular one of the workstations that worked on the workpiece.

BACKGROUND OF THE INVENTION

The present invention generally relates to the identification ofworkpieces and more specifically to a method of identifying workstationsthat performed work on a workpiece.

It is known to provide a marking system that marks a finished workpieceto identify the model of the workpiece, the production run that producedthe workpiece and/or the order of production of the workpiece. Anexample of such a marking process for a vehicle frame is disclosed inU.S. Pat. No. 5,202,836 to lida et al., which is assigned to theassignee of the present application. If a defect later appears in theworkpiece, such a mark helps identify when the workpiece was finished,which provides some help in identifying the source of the defect. In atypical manufacturing operation, however, a plurality of workstationswork on a workpiece. Moreover, there are typically a plurality ofworkstations that perform the same operation or process. Thus, aworkpiece may, for example, have a particular drilling operationperformed on it by one of a plurality of drilling machines. As a result,even if the particular drilling operation is identified as the source ofa defect in the workpiece, the defect may have been caused by any one ofthe drilling machines. Conventional marking systems, such as the typeidentified above, fail to provide a mark or marks that can identify aparticular workstation as having performed an operation on a particularworkpiece.

Accordingly, there is a need in the art for a method of identifyingworkstations that performed work on a workpiece. The present inventionis directed to such a method.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method is provided foridentifying workstations that performed work on a workpiece in a workline having a plurality of zones, wherein each zone includes a pluralityof workstations that perform the same type of operation. In accordancewith the method, a unique code is provided for identifying eachworkstation. After work is performed on the workpiece in one of theworkstations in one of the zones, the workpiece is marked with theunique code for the workstation. The workpiece is then moved to afollowing zone. This procedure is repeated for the other zones in thework line. Each of the unique codes is a mark and the location of themark on the workpiece.

In accordance with the present invention, in a first one of the zones, aworkpiece is moved from a first input area to a first workstation. Theworkpiece is worked on in the first workstation and then is moved to afirst output area in the first one of the zones. At the first outputarea, the workpiece is marked with a first mark indicating that thefirst workstation worked on the workpiece. The workpiece is then movedto a second input area in a second one of the zones and from there, ismoved to a second workstation in the second one of the zones. Theworkpiece is worked on in the second workstation and then is moved to asecond output area in the second one of the zones. At the second outputarea, the workpiece is marked with a second mark indicating that thesecond workstation worked on the workpiece. The workpiece is moved tothe first workstation and to the first output area by a firstautoloader, while the workpiece is moved to the second workstation andto the second output area by a second autoloader.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects, and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 shows a side elevational view of an autoloader;

FIG. 2 shows a top plan view of a portion of a machining line includingthe autoloader;

FIG. 3 shows a perspective view of a portion of the autoloader and aquality control station;

FIG. 4 shows a front view of a control panel for the quality controlstation;

FIG. 5 shows a flow chart of a portion of a supply routine;

FIG. 6 shows a flow chart of another portion of the supply routine;

FIG. 7 shows a flow chart of a quality control routine;

FIG. 8 is a diagram graphically showing how the supply routine operates;

FIG. 9 is a schematic view of a crankshaft disposed at a drop-offstation adjacent to a stamping machine;

FIG. 10 is an end view of a first end of a crankshaft showing markingareas and positions; and

FIG. 11 is an end view of a second end of a crankshaft showing markingareas and positions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It should be noted that in the detailed description that follows,identical components have the same reference numerals, regardless ofwhether they are shown in different embodiments of the presentinvention. It should also be noted that in order to clearly andconcisely disclose the present invention, the drawings may notnecessarily be to scale and certain features of the invention may beshown in somewhat schematic form.

As used herein, the term “chronological order” shall mean the order inwhich events occur, beginning with the oldest event first and endingwith the most current event.

The present invention is directed to a method of identifyingworkstations that performed work on a workpiece during a production runin which workpieces are supplied to the workstations by workpiececonveyance apparatus. The conveyance apparatus may be an autoloader,such as an autoloader 10 shown best in FIG. 1. The autoloader 10 isoperable to move workpieces to and from a plurality of workstations MC1,MC2, MC3, MC4 and to load and unload the workpieces into and from theworkstations MC1-MC4. The workstations MC1-MC4 may be machines groupedin a zone 20 of a machining line 22, such as a machining line forproducing automotive crankshafts. In such an application, the workpiecesare automotive crankshafts and the workstations MC1-MC4 in the zone 20perform machining operations on the crankshafts. Preferably, theworkstations MC1-MC4 all perform the same machining operation. Forpurposes of illustration, the workstations MC1-MC4 may all be drillingmachines for drilling cross oil passage holes in a crankshaft. It shouldbe appreciated, however, that the present invention is not limited to aparticular operational environment, such as a crankshaft machining line,but rather has numerous applications, as will be understood by those ofskill in the art.

Referring now to FIG. 2, the machining line 22 includes a plurality ofzones in addition to the zone 20. For purposes of brevity, however, onlya portion of the zones are shown. More specifically, only the zone 20and a preceding zone 24 and a following zone 26 are shown. As set forthabove, the zone 20 includes the autoloader 10, which servicesworkstations MC1-MC4. The zone 20, however, also includes a secondautoloader 28 and workstations MC5, MC6, MC7 and MC8. The preceding andfollowing zones 24, 26 include autoloaders 30, 32 respectively, and theother zones each have at least one autoloader, as well. The autoloaders28, 30, 32 and the other autoloaders have substantially the sameconstruction and operation as the autoloader 10, whose construction andoperation will be discussed in more detail below. The zone 20 isconnected to the preceding zone 24 by an input conveyor 34 and isconnected to the following zone 26 by an output conveyor 36. The inputconveyor 34 is operable to support and carry workpieces that have beenworked upon in the preceding zone 24 to the zone 20, whereas the outputconveyor 36 is operable to support and carry workpieces that have beenworked upon in the zone 20 to the following zone 26. The workpieces arepreferably disposed on pallets when they are carried by the input andoutput conveyors 34, 36.

The input and output conveyors 34, 36 may be conventional rollerconveyors supported above a floor 38. In addition to moving workpieces,the input and output conveyors 34, 36 act as buffers to hold workpieces.For example, if all or a portion of zone 20 is taken down formaintenance or other reasons, the output conveyor 36 should havesufficient capacity to hold workpieces from zone 20 to continue feedingthe workpieces to following zone 26. In this manner, the downtime onzone 20 will have minimum impact on following zone 26. Since thecapacity to hold workpieces is determined by the lengths of the inputand output conveyors 34, 36, the lengths of the input and outputconveyors 34, 36 are selected to provide a desired amount of buffering.

As set forth above, the machining line 22 may produce automotivecrankshafts and in accordance therewith, the workstations M1-M8 in zone20 may all be drilling machines for drilling cross oil passage holes ina crankshaft. In such an application, the preceding zone 24 may includea plurality of workstations MC9, MC10, MC11, which are gundrill machinesfor drilling slant oil passage holes, and the following zone 26 mayinclude a plurality of workstations MC12, MC13, which are multiwheelgrind machines for grinding main journals and post ends of a crankshaft.

When a workpiece moves through the machining line 22, only oneworkstation in a zone works on the workpiece. After the workpiece isworked on in a zone by one of the workstations located therein, theworkpiece is then moved to a succeeding zone, where the workpiece isworked on by one of the workstations located therein. This procedurecontinues until the workpiece travels through the entire machining line22 and is thereby finished. Thus, with regard to the portion of themachining line shown in FIG. 2, a workpiece is worked on by one of theworkstations MC9, MC10, MC11 in the preceding zone 24 and then is movedby the autoloader 30 and the input conveyor 34 to the zone 20. In zone20, the workpiece is worked on by one of the workstations MC1-MC8 andthen is moved by the autoloader 10 or the second autoloader 28 and theoutput conveyor 36 to the following zone 26. In the following zone 26,the workpiece is worked on by one of the workstations MC12 and MC13 andthen is moved to the next zone.

Each of the workstations MC1-M13 and the other workstations in themachining line 22 is operable to generate a call signal indicating thatthe workstation is ready to receive and work upon a workpiece(crankshaft). Each of the workstations MC1-M13 and the otherworkstations in the machining line 22 is also operable to generate anerror signal indicating that there is a problem with the workstation orthe workstation is off-line and that a workpiece (such as a crankshaft)should not be loaded into the workstation. A control system 40 for theautoloader 10 is electrically connected by wiring (not shown) to theworkstations MC1-MC4 and is operable to receive the call and errorsignals from the workstations MC1-MC4. As will be discussed furtherbelow, the control system 40 uses the call and error signals to controlthe operation of the autoloader 10.

In the zone 20, the workstations MC1-MC8 are spaced apart and arrangedin a pair of lines. Similarly in the preceding zone 24, the workstationsMC9-11 are spaced apart and arranged in a line, and in the followingzone 26, the workstations MC12, MC13 are spaced apart and arranged in aline. The zone 20, the preceding zone 24 and the following zone 26 arearranged in a parallel and spaced-apart manner. Thus, the input andoutput conveyors 34, 36 extend in perpendicular fashion between thepreceding zone 24 and the zone 20 and the zone 20 and the following zone26, respectively. The input and output conveyors 34, 36 are disposedrelatively close to each other, toward a conveyor end 20 a of the zone20.

Referring back to FIG. 1 and now also to FIG. 3, the autoloader 10includes a carriage 50 that is mounted to, and movable along, a guidancestructure that defines a path of travel between the workstationsMC1-MC4. The guidance structure can include at least one rail, such asan overhead monorail 52 supported on pillars 54 extending upwardly fromthe floor 38, as shown. Alternately, the monorail 52 can be suspendedfrom a ceiling. The carriage 50 is moved along the monorail 52 by aservomotor (not shown). The carriage 50 is provided with a lowerator 56for loading and unloading workpieces to and from the workstationsMC1-MC4. The lowerator 56 is driven by pneumatic cylinders or otherdrive means to vertically move between an upper or travel position and alower or servicing position. The lowerator 56 includes a pair ofgrippers 58, 60 for holding workpieces. The carriage 50 is connected tothe control system 40 by wiring 62. As will be discussed further below,the control system 40 is operable to control the movement of thecarriage 50 along the monorail 52 and to control the movement andoperation of the lowerator 56 and the grippers 58, 60.

The monorail 52 is spaced above and extends over the workstationsMC1-MC4. Since the workstations MC1-MC4 are arranged in a line, themonorail 52 is linear. It should be appreciated, however, that if theworkstations MC1-MC4 are arranged in a different configuration, themonorail 52 will have a correspondingly different configuration, aswell. Each workstation MC1-MC4 has an entrance area that faces upwardlytoward the monorail 52. As will be described further below, workpiecesare loaded into the workstations MC1-MC4 by the lowerator 56 through theentrance areas. At each of the workstations MC1-MC4, a shutter door 64is disposed between the monorail 52 and the entrance area of theworkstation. Each shutter door 64 is movable between a closed position,wherein the shutter door 64 is disposed between the monorail 52 and theentrance area, and an open position, wherein the shutter door 64 is notdisposed between the monorail 52 and the entrance area. When the shutterdoor 64 of one of the workstations MC1-MC4 is in the closed position,the shutter door 64 prevents the lowerator 56 from entering theworkstation through the entrance area. Each shutter door 64 is providedwith a set of electrical contacts that are electrically connected to thecontrol system 40 for the autoloader 10. The electrical contacts areoperable to provide the control system 40 with control signals thatinform the control system 40 whether the shutter door 64 is open orclosed.

Referring back to FIG. 2, at the end of the input conveyor 34 is a firstinput area 66, which is a vertically-movable substrate from which theautoloader 10 obtains workpieces for loading into the workstationsMC1-MC4. At the end of the output conveyor 36 is a second input area 70,which is a vertically-movable substrate from which the autoloader 32obtains workpieces for loading into the workstations MC12 and MC13. Thefirst and second input areas 66, 70 are each moved by a pneumaticcylinder or other lift means. It should be noted that the other zones inthe machining line 22 also have one or more input areas from which theautoloader(s) in the zones obtain workpieces.

At the beginning of the output conveyor 36 is a drop-off station 68.Similarly, at the beginning of an ouput conveyor 72 for the followingzone 26 is a second drop-off station 74. Drop-off station 68 is avertically-movable substrate upon which workpieces from the workstationsMC1-MC4 are deposited by the autoloader 10, while second drop-offstation 74 is a vertically-movable substrate upon which workpieces fromthe workstations MC12 and MC13 are deposited by the autoloader 32. Itshould be noted that the other zones in the machining line 22 also haveone or more drop-off stations for receiving workpieces from theautoloader(s) in the zones.

Referring now also to FIG. 9, the drop-off station 68 is moved by apneumatic cylinder 76 or other lift means. The drop-off station 68 ismovable between a lowered position and a raised position. When thedrop-off station 68 is moved to the lowered position, a workpiece (suchas a crankshaft 250) disposed on the drop-off station 68 moves onto theoutput conveyor 36. When the drop-off station 68 is in the raisedposition, a workpiece disposed on the drop-off station 68 is accessibleby a stamping machine 80. Although not shown, the second drop-offstation 74 and the other drop-off stations in the machining line 22 havethe same or substantially the same construction as the drop-off station68 and are accessible by stamping machines (having the same orsubstantially the same construction as the stamping machine 80) or othertype of marking device. For example, in lieu of a stamping machine, azone may have a drill that marks the workpiece with small holes.

The stamping machine 80 is preferably a pneumatic pin marking machine,such as is available from Telesis Controls Corporation. The stampingmachine 80 may be constructed in accordance with U.S. Pat. No.4,506,999, which is hereby incorporated by reference. The stampingmachine 80 uses an array of pneumatically driven marker pins to make aplurality of indentations in a workpiece so as to form a stamp or mark.The stamping machine 80 is operatively connected to the control system40 for receiving command signals therefrom. The stamping machine 80 isoperable to form a mark for each of the workstations MC1-MC4. As will bediscussed further below, when the autoloader 10 moves a workpiece fromone of the workstations MC1-MC4 to the drop-off station 68, the stampingmachine 80 stamps the workpiece with a mark identifying the workstation.Similarly, when the autoloader 32 moves a workpiece from one of theworkstations MC12 and MC13 to the second drop-off station 74, thestamping machine disposed adjacent thereto stamps the workpiece with amark identifying the workstation. This same procedure occurs at each ofthe drop-off stations in the machining line 22 having a stampingmachine.

A quality control (QC) station 90 is located toward the output conveyor36, near the drop-off station 68. Referring now to FIG. 3, the QCstation 90 includes a cage 92 defining an interior space 94 forreceiving the lowerator 56 of the carriage 50. A tray 96 with pivotablecover 98 is secured to a front wall of the cage 92. A workpiece jig 100is movably mounted to the cage 92 and is movable between a retractedposition, wherein the workpiece jig 100 is disposed in the interiorspace 94 of the cage 92, and an extended position, wherein the workpiecejig 100 is disposed in the tray 96. When the workpiece jig 100 is in theretracted position, the workpiece jig 100 is positioned to receive aworkpiece from the lowerator 56. The workpiece jig 100 is constructed tohold a workpiece, such as a crankshaft.

Referring now also to FIG. 4, a quality control (QC) panel 102 isdisposed proximate to the QC station 90. The QC panel 102 includes aplurality of operator interface devices in the form of a main selectorswitch 104, a lamp check light 106, a plurality of lighted requestpushbuttons 108 a, 108 b, 108 c, 108 d and a plurality of lighted bypasspushbuttons 110 a, 110 b, 110 c, 110 d. The operator interface devicesare electrically connected to the control system 40 by wiring (notshown) and are operable to transmit control signals to the controlsystem 40 in response to manipulation by an operator, as will be furtherdescribed below. The main selector switch 104 is operable to select adesired QC function and is movable between a “LOAD” position, an“UNLOAD” position and a “CVYR” position. The request pushbuttons 108 a-dare operable for selecting the workstation for which the QC function isdesired, while the bypass pushbuttons 110 a-d are operable for putting adesired workstation in a bypass mode.

The main selector switch 104 operates in conjunction with the requestpushbuttons 108 a-d to generate QC signals for the workstations MC1-MC4.For example, when the main selector switch 104 is set to the LOADposition and the request pushbutton 108 a for MC1 is depressed, aworkstation load signal is generated for MC1 and transmitted to thecontrol system 40. When the main selector switch 104 is set to theUNLOAD position and the request pushbutton 108 b for workstation MC2 isdepressed, a workstation unload signal is generated for workstation MC2and transmitted to the control system 40. When the main selector switch104 is set to the CVYR position and the request pushbutton 108 c forworkstation MC3 is depressed, a drop-off signal is generated forworkstation MC3 and transmitted to the control system 40.

The control system 40 uses the workstation load signal, the workstationunload signal and the drop-off signal to control the autoloader 10 tomove workpieces to and from the QC station 90, as will be discussed inmore detail below. Briefly, however, when a workstation load signal isreceived for, say workstation MC1, the control system 40 controls theautoloader 10 such that the autoloader 10 completes its current cycleand then picks up a workpiece from the QC station 90 and moves it toworkstation MC1. When a workstation unload signal is received for, sayworkstation MC2, the control system 40 controls the autoloader 10 suchthat the autoloader 10 completes its current cycle and then picks up aworkpiece from workstation MC2 and moves it to the QC station 90. When adrop-off signal is received for, say workstation MC3, the control system40 controls the autoloader 10 such that the autoloader 10 completes itscurrent cycle and then picks up a workpiece from the QC station 90 andmoves it to the drop-off station 68, where the workpiece is stamped bythe stamping machine 80 with a mark indicating that the workpiece wasworked on by workstation MC3, as will be described more fully below.

When the control system 40 receives a workstation load signal or aworkstation unload signal for one of the workstations MC1-MC4, thecontrol system 40 places the workstation in a bypass mode, which isindicated by a flashing light on the lighted bypass pushbutton 110 forthe workstation. When one of the workstations MC1-MC4 is in the bypassmode, an error signal is generated for the workstation and transmittedto the control system 40. As will be described further below, when thecontrol system 40 receives an error signal from one of the workstationsMC1-MC4, the control system 40 removes the workstation from theautoloader supply routine 120, i.e., the control system 40 controls theautoloader 10 so that it will not supply workpieces to the workstation.

Each of the workstations MC1-MC4 can also be placed in the bypass modeby depressing the bypass pushbutton 110 for the workstation. After oneof the workstations MC1-MC4 is placed in the bypass mode by either thecontrol system 40 or by the depression of its bypass pushbutton 110, theworkstation stays in the bypass mode until the operator restarts theworkstation. If the workstation was placed in the bypass mode for aninspection of one the workpieces the workstation worked on, the operatortypically does not restart the workstation until after the operatorverifies the quality of the workpiece.

The foregoing control scheme is used to inspect workpieces for qualitycontrol purposes. For example, if an operator desires to check thequality of the operation performed by workstation MC1, the operatormoves the workpiece jig 100 to the retracted position, then moves themain selector switch 104 to “UNLOAD” and depresses the requestpushbutton 108 a for MC1. In response, the autoloader 10 completes itscurrent cycle and then delivers a workpiece that has been worked upon inworkstation MC1 to the workpiece jig 100 at the QC station 90. Theworkstation MC1 is then placed in the bypass mode by the control system40. The operator then moves the workpiece jig 100 to the extendedposition and opens the cover 98. The operator may inspect the workpiecewhile it is being held by the workpiece jig 100, or, more preferably,the operator may inspect the workpiece outside the tray 96 on a standalone jig (not shown). The operator preferably uses a hoist (not shown)located outside the cage 92 to move the workpiece to the stand alonejig. When the workpiece is situated in the desired inspection location,the operator inspects the workpiece, such as for compliance with certainspecifications. If the workpiece passes the inspection (such as by fullymeeting the specifications), the operator loads the workpiece back intothe workpiece jig 100 and moves the work piece jig 100 to the retractedposition. The operator then moves the main selector switch 104 to the“CVYR” position and depresses the request pushbutton 108 a forworkstation MC1. In response, the autoloader 10 completes its currentcycle and then delivers the inspected workpiece to the drop-off station68, where it is stamped with a mark indicating that the workpiece wasworked on by workstation MC1. The operator then restarts the MCIworkstation to take it out of the bypass mode.

If the workpiece does not pass inspection (such as by not meeting thespecifications), but the operator believes that the workpiece can passinspection if the workpiece is reworked in MC1 (or another desiredworkstation), the operator loads the workpiece back into the workpiecejig 100 and moves the work piece jig 100 to the retracted position. Theoperator then moves the main selector switch 104 to the “LOAD” positionand depresses the request pushbutton 108 a for workstation MC1 (or therequest pushbutton for the other desired workstation). In response, theautoloader 10 completes its current cycle and then returns the inspectedworkpiece back to workstation MC1 (or delivers it to the other desiredworkstation), where it is reworked.

If, from inspection, the operator determines that the workpiece does notmeet the specifications and cannot be reworked, the operator simplymoves the workpiece to a scrap area (not shown).

Wherever practical, a quality control (QC) station is provided for eachof the other autoloaders in the machining line 22. In this manner, mostzones in the machining line 22 have at least one QC station. If thenature of a zone or subzone serviced by an autoloader is such that aworkpiece can easily be inspected on an output conveyor and theworkpiece will not be returned to the zone or subzone for rework, a QCstation is not provided for the autoloader in the zone or sub-zone. Foreach of the autoloaders in the zones and sub-zones having a QC station,the QC station is preferably located toward a conveyor end of theautoloader, i.e., the end of the autoloader disposed next to input andoutput conveyors.

With regard to the portion of the machining line 22 shown in FIG. 2, aQC station 112 is provided for the second autoloader 28, while a QCstation 114 is provided for the autoloader 30 in the preceding zone 24and a QC station 116 is provided for the autoloader 32 in the followingzone 26. The QC stations 112-116 and the other QC stations in themachining line 22 preferably have substantially the same constructionand operation as the QC station 90. Quality control (QC) panels (notshown) having substantially the same construction and operation as theQC panel 102 are disposed proximate to the QC stations 112-116 and theother QC stations in the machining line 22, respectively. These QCpanels are operably connected to control systems for the secondautoloader 28, the autoloaders 30, 32 and the other autoloaders, andinteract with the control systems in substantially the same manner thatthe QC panel 102 interacts with the control system 40. In this regard,it should be noted that the control systems for the second autoloader28, the autoloaders 30, 32 and the other autoloaders have substantiallythe same construction and operation as the control system 40.

The control system 40 for the autoloader comprises a programmable logiccontroller (PLC). A Q series PLC from Mitsubishi Automation, and, morespecifically, a Mitsubishi Q2AS CPU s-1, has been found suitable for useas the PLC. The PLC includes a base unit having a plurality of power,processing and input/out (I/O) modules mounted therein. Morespecifically, the base unit includes a CPU module, a power supplymodule, one or more input modules, one or more output modules and one ormore positioning modules that are connected together by a plurality ofinternal buses. The input, output and positioning modules areelectrically connected by wiring to the carriage 50, the shutter doors64 and other devices in the zone 20 and are operable to transmit andreceive signals to and from the foregoing. More specifically, the inputmodule(s) are connected by wiring to the contacts of the shutter doors64 and other devices to receive status information therefrom, while theoutput modules are connected by wiring to the drive means for thelowerator 56 and other devices to provide commands thereto. Thepositioning module(s) are connected to the servo motor for the carriage50 and other servo devices of the autoloader 10 to control the same inconjunction with commands from the CPU module.

The CPU module implements control strategies for the autoloaderutilizing a control program written in a PLC language or a combinationof PLC languages. Suitable PLC languages include ladder diagram,structured text, function block diagram, instruction list and sequentialfunction (or flow) chart (SFC) and combinations of the foregoing.Preferably, the control program and the PLC language(s) are compatiblewith IEC61131 standards. When a Mitsubishi Q2AS CPU s-1 is used, aladder diagram language that utilizes function blocks (applicationinstructions) may be used as the PLC language. One of the applicationinstructions that is used in the present invention is known as the FIFWinstruction, which creates a data table and writes data to the end ofthe table with each execution of the instruction. A software packageavailable from Mitsubishi Automation under the tradename GPP-WIN is usedto program a Mitsubishi Q2AS CPU s-1 PLC.

The control system 40 is connected to by the wiring 62 to the carriage50 for transmitting and receiving control signals to and from thecarriage 50. The control system 40 is operable to control the movementof the carriage 50 along the monorail 52 and to control the operation ofthe lowerator 56 and the grippers 68, 60. With regard to each of theworkstations MC1-MC4, the control system 40 is operable to control thecarriage 50 and the grippers 58, 60 such that the carriage 50 can loadand unload workstation MC1 in the manner described below. First, thegripper 58 grasps a workpiece in the input area 66 and then thelowerator 56 (with the workpiece) moves upward to the travel position.While the lowerator 56 is in the travel position, the carriage 50 movesto the workstation MC1. The lowerator 56 then moves downward to theservicing position, wherein the grippers 58, 60 enter the workstationMC1 through the entrance area. The gripper 60 grasps a worked-uponworkpiece that is already present in the workstation MC1 and thenremoves the worked-upon workpiece from the workstation MC1. The gripper58 loads the workpiece from the input area 66 into the workstation MC1and then the lowerator 56 (with the worked-upon workpiece) moves upwardinto the travel position. While the lowerator 56 is in the travelposition, the carriage 50 moves to the drop-off station 68. At thedrop-off station 68, the lowerator 56 moves downward to the servicingposition and the gripper 60 releases the worked-upon workpiece so as todeposit the worked-upon workpiece at the drop-off station 68. Theworked-upon workpiece is then stamped by the stamping machine 80 with astamp indicative of the workstation MC1.

The control program of the control system 40 controls the provision ofworkpieces to the workstations by the autoloader 10. Initially, itshould be noted that in the control program, each of the workstationsMC1-MC4 is assigned a tag in the form of a unique fixed number. Wheneverthe control system 40 receives a call signal from one of theworkstations MC1-MC4, the control program enters the tag for theworkstation that transmitted the call signal into a FIFO data table (atstep 125 of the supply routine 120 described below) using an FIFWapplication instruction. As set forth above, the FIFW instruction entersthe tag at the end of the FIFO data table. In this manner, tags in thedata table are arranged in chronological order, i.e., the workstationtag for the oldest received call signal is disposed at the beginning ofthe data table. Whenever the control system 40 receives an error signalfrom a workstation whose tag is entered in the FIFO data table, thecontrol program removes the tag from the FIFO data table.

The control program controls the provision of workpieces to theworkstations MC1-MC4 in accordance with the order in which call signalsare received from the workstations MC1-MC4. More specifically, thecontrol program in the CPU module controls the autoloader 10 using asupply routine 120 depicted by the flowchart shown in FIGS. 5 and 6. Atstep 121, the supply routine 120 initiates. At step 122, the autoloader10 is located in the input area 66, the gripper 58 is holding a selectedone of the workpieces and the supply routine 120 looks for a call signalfrom one of the workstations MC1-MC4. Next, in decision step 124, thesupply routine 120 determines if a call signal from a workstation hasbeen received. If the supply routine 120 determines that a call signalhas not been received, the supply routine 120 moves back to step 122. Ifa call signal has been received, the supply routine 120 moves to step125, where the supply routine 125 enters the tag for the workstationthat transmitted the call signal into the FIFO data table. At step 126,the supply routine 120 selects the tag at the top of the FIFO data table(which corresponds to the oldest received call signal). At step 128, theselected tag is removed from the data table. Continuing, the supplyroutine 120 moves to step 130 and generates a movement command signalthat is transmitted to the autoloader 10 and causes the carriage 50 tomove to a wading position located over a selected one of theworkstations that corresponds to the selected tag. At step 132, thesupply routine 120 looks to see if the control system 40 has receivedany signals from the selected workstation. Next, in decision step 134,the supply routine 120 determines if the control system 40 has receiveda ready signal, an error signal, or a shutter door 64 closed signal fromthe selected workstation. If the supply routine 120 determines that nosignals have been received, the supply routine 120 moves back to step132. If the supply routine 120 determines that an error signal or ashutter door 64 closed signal has been received, the supply routine 120moves back to step 124 (however, the carriage 50 maintains its positionover the current selected one of the workstations and remains thereuntil another movement command signal is received from step 130). If thesupply routine 120 determines that a ready signal has been received fromthe selected workstation, the supply routine 120 moves to step 136 andgenerates an unload/load command signal that is transmitted to theautoloader 10. In response to the unload/load command, the lowerator 56moves downward to the servicing position. The gripper 60 then removesany worked-upon workpiece from the selected workstation and the gripper58 loads the selected workpiece into the workstation. The lowerator 56then moves upward to the travel position. Once the lowerator 56 is inthe travel position, the supply routine 120 moves to decision step 138,wherein the supply routine 120 determines whether the gripper 60 has aworked-upon workpiece. If the supply routine 120 determines that thegripper 60 does not have a worked-upon workpiece, the supply routine 120moves ahead to step 146. If the supply routine 120 determines that thegripper has a worked-upon workpiece, the supply routine 120 moves tostep 140, wherein the supply routine 120 generates a second movementcommand that is transmitted to the autoloader 10 and causes the carriage50 to move to the drop-off station 68. When the carriage 50 is at thedrop-off station 68, the supply routine 120 moves to a subsequent step142 and generates a deposit command that is transmitted to theautoloader 10. In response to the deposit command, the lowerator 56moves downward to the servicing position and the gripper 60 deposits theworked-upon workpiece on the drop-off station 68. The lowerator 56 thenmoves upward to the travel position. At step 144, the supply routine 120generates a stamp signal that is transmitted to the stamping machine 80located at the drop-off station 68. In response to the stamp signal, thestamping machine 80 stamps the worked-upon workpiece with a markindicating that the worked-upon workpiece was worked on by the selectedworkstation.

After step 144, the supply routine 120 moves to step 146 and generates athird movement command that is transmitted to the autoloader 10 andcauses the carriage 50 to move to the input area 66. Once the carriage50 is in the input area 66, the supply routine 120 moves to decisionstep 148, wherein the supply routine 120 determines whether a QC signalhas been received. If the supply routine 120 determine that no QC signalhas been received, the supply routine 120 moves to step 150 andgenerates a pick-up command that is transmitted to the autoloader 10. Inresponse to the pick-up command, the lowerator 56 moves downward to theservicing position and the gripper 58 picks up another selected one ofthe workpieces from the input area 66. The lowerator 56 then movesupward to the travel position. At this point, the supply routine 120moves back to step 122.

If, at decision step 148, the supply routine 120 determines that a QCsignal has been received, the control program moves to a QC routine 200depicted by the flowchart shown in FIG. 7. At decision steps 202, 204,206, the QC routine 200 respectively determines whether the QC signal isa workstation unload signal, a workstation load signal, or a drop-offsignal.

If, at step 202, it is determined that a workstation unload signal isreceived, the QC routine 200 moves to step 208 and generates a QCmovement command that is transmitted to the autoloader 10. In responseto the QC movement command, the carriage 50 moves to a selected one ofthe workstations for which the workstation unload signal wastransmitted. At step 210, the QC routine 200 generates and transmits aQC unload command to the autoloader 10, which causes the lowerator 56 tomove downward to the servicing position. The gripper 58 then removes ato-be-inspected workpiece from the selected workstation and thelowerator 56 moves upward to the travel position. At step 212, the QCroutine 200 generates and transmits a second QC movement command to theautoloader 10, which causes the carriage 50 to move to the QC station90. Next, the QC routine 200 moves to step 214, wherein the QC routine200 generates and transmits a QC deposit command, which causes thelowerator 56 to move downward to the servicing position. The gripper 58then deposits the to-be-inspected workpiece at the QC station 90. Thelowerator 56 then moves up to the travel position. At step 216, the QCroutine 200 generates and transmits to the autoloader 10 a QC returncommand. In response, the carriage 50 moves to the input area 66. Oncethe carriage 50 is at the input area 66, the QC routine 200 moves tostep 218, wherein the QC routine 200 places the selected workstationinto bypass mode. After step 218, the control program moves back to step150 of the supply routine 120.

If, at step 204, it is determined that a workstation load signal isreceived, the QC routine 200 moves to step 222 and generates a QCmovement command that is transmitted to the autoloader 10. In responseto the QC movement command, the carriage 50 moves to the QC station 90.Next, the QC routine 200 moves to step 224, wherein the QC routine 200generates and transmits a QC removal command, which causes the lowerator56 to move downward to the servicing position. The gripper 58 thenremoves a to-be-reworked workpiece from the QC station 90 and thelowerator 56 moves upward to the travel position. At step 226, the QCroutine 200 generates and transmits a second QC movement command to theautoloader 10, which causes the carriage 50 to move to a selected one ofthe workstations for which the workstation load signal was transmitted.Next, the QC routine 200 moves to step 228, wherein the QC routine 200generates and transmits a QC unload/load command, which causes thelowerator 56 to move downward to the servicing position. The gripper 60then removes a worked-upon workpiece from the selected workstation andthe gripper 58 deposits the to-be-reworked workpiece at the selectedworkstation. The lowerator 56 then moves up to the travel position. Atstep 229, the QC routine 200 generates and transmits a third QC movementcommand to the autoloader 10, which causes the carriage 50 to move tothe drop-off station 68. Next, the QC routine 200 moves to step 230,wherein the QC routine 200 generates and transmits a QC deposit command,which causes the lowerator 56 to move downward to the servicingposition. The gripper 60 then deposits the worked-upon workpiece in thedrop-off station 68. The lowerator 56 then moves up to the travelposition. At step 231, the QC routine 200 generates a stamp signal thatis transmitted to the stamping machine 80 located at the drop-offstation 68. In response to the stamp signal, the stamping machine 80stamps the worked-upon workpiece with a mark indicating that theworked-upon workpiece was worked on by the workstation for which theworkstation load signal was transmitted. At step 232, the QC routine 200generates and transmits to the autoloader 10 a QC return command. Inresponse, the carriage 50 moves to the input area 66. Once the carriage50 is at the input area 66, the QC routine 200 moves to step 233,wherein the QC routine 200 places the selected workstation into bypassmode. After step 233, the control program moves back to step 150 of thesupply routine 120.

If, at step 206, it is determined that a drop-off signal is received,the QC routine 200 moves to step 234 and generates a QC movement commandthat is transmitted to the autoloader 10. In response to the QC movementcommand, the carriage 50 moves to the QC station 90. Next, the QCroutine 200 moves to step 236, wherein the QC routine 200 generates andtransmits a QC removal command, which causes the lowerator 56 to movedownward to the servicing position. The gripper 58 then removes acompliant workpiece from the QC station 90 and the lowerator 56 movesupward to the travel position. At step 238, the QC routine 200 generatesand transmits a second QC movement command to the autoloader 10, whichcauses the carriage 50 to move to the drop-off station 68. Next, the QCroutine 200 moves to step 240, wherein the QC routine 200 generates andtransmits a QC deposit command, which causes the lowerator 56 to movedownward to the servicing position. The gripper 58 then deposits thecompliant workpiece in the drop-off station 68. The lowerator 56 thenmoves up to the travel position. At step 242, the QC routine 200generates a stamp signal that is transmitted to the stamping machine 80located at the drop-off station 68. In response to the stamp signal, thestamping machine 80 stamps the compliant workpiece with a markindicating that the compliant workpiece was worked on by the workstationfor which the drop-off signal was transmitted. After step 242, the QCroutine 200 moves to step 244, wherein the QC routine 200 generates areturn command and transmits it to the autoloader 10, which causes thecarriage 50 to move to the input area 66. Once the carriage 50 is at theinput area 66, the control program moves back to step 150 of the supplyroutine 120.

The operation of the supply routine 120 will now be explained withreference to FIG. 8. In all of the frames A, B, C, call signals from theworkstations MC1-MC4 are received by the control system 40 in the orderMC2, MC4, MC3, MC1, MC2, MC4, MC3, MC1. In frame A, normal operation ofthe autoloader 10 is depicted. The control system 40 controls theautoloader 10 to supply the workstations MC1-MC4 with workpieces in theorder in which the call signals are received, namely MC2, MC4, MC3, MC1.In frame B, MC2 sends an error signal to the control system 40 at thesame time or very soon after it sends its call signal. The error signalcauses the control program to remove the tag for MC2 from the FIFO datatable. As a result, when the supply routine 120 moves to step 126 andselects the tag at the top of the FIFO data table, the supply routine120 will select the tag for MC4 (which has now moved to the top, sincethe tag for MC2 has been removed). Accordingly, the control system 40controls the autoloader 10 to supply workpieces in the order MC4, MC3,MC1. In frame C, MC1 sends an error signal to the control system 40after the carriage 50 has moved to the waiting position over MC1 afterstep 130 of the supply routine 120. At step 132, however, the supplyroutine 120 finds the error signal. Therefore, at step 134, the supplyroutine 120 moves back to step 124. At step 126, supply routine 120selects the tag currently at the top of the FIFO data table, which isthe tag for MC2. Accordingly, the control system 40 controls theautoloader 10 to supply workpieces in the order MC2, MC4, MC3, MC2.

Routines substantially similar to the supply routine 120 and the QCroutine 200 described above are performed by the control systems for theautoloaders 28, 30, 32 and other autoloaders in the machining line 22.Thus, when a workpiece travels from zone to zone, the workpiece isstamped with markings in a manner indicating the workstations thatworked on the workpiece in each of the zones. Preferably, the markingsare made in accordance with predetermined unique codes for theworkstations, wherein each unique code is a combination of the locationof a mark on the workpiece and the type or nature of the mark. Morespecifically, the workpiece includes a plurality of marking areas andpositions, wherein each area or position in an area represents a zone inthe machining line 22. The mere presence of a mark in a marking area orposition in a marking area indicates a particular zone. The type ornature of the mark specifies the particular machine in the zone. Themarking areas are selected based on a number of criteria, such as: (i.)not being in a critical location that would affect the utility of theworkpiece, (ii.) being in a location where markings will not be machinedoff in future operations, (iii.) when the workpiece sits on the outputconveyor 36 (and other output conveyors), the marking areas are visibleto operators, and (iv.) being in a location that can easily be seen whenthe workpiece is in a heat treatment basket (if the operation is beforeheat treatment).

With specific regard to the workpiece being a crankshaft, such as acrankshaft 250 (shown in FIGS. 9-11), the crankshaft 250 is providedwith a plurality of stamp marking areas 252, 254, 256, 258, 260, 262,264, within which the stamping machine 80 and other stamping machines ofthe machining line 22 make marks. Stamp marking areas 252, 254 and 256are located on a counterweight 266 (shown in FIG. 10), located toward afirst end of the crankshaft 250, while stamp marking areas 258, 260,262, 264 are located on a counterweight 268 (shown in FIG. 11), locatedtoward an opposing second end of the crankshaft 250. Stamp marking areas252-256 each contain a plurality of positions, wherein each positionrepresents a zone. Stamp marking areas 258-264 each only contain oneposition and, thus, each represent a zone. In stamp marking area 254,position A represents a zone of the machining line 22 that is not shown,such as a zone containing a pair of burnish machines, while position Brepresents the preceding zone 24 and position C represents the zone 20.In stamp marking area 256, positions A, C and D represent zones of themachining line 22 that are not shown, such as a zone containingmultiwheel grinders, a zone containing pin grinders and a zonecontaining flange grinders, respectively, while position B representszone 26.

Preferably, the marks made by the stamping machine 80 and other stampingmachines in the machining line 22 are numeric characters, morepreferably single digit numerals. For example, in zone 20, the marks forworkstations MC1-MC8 may be 1-8, respectively, in the preceding zone 24,the marks for workstations MC9-MC11 may be 1-3, respectively, and in thefollowing zone 26, the marks for workstations MC12 and MC13 may be 1 and2, respectively. In this regard, it should be noted that the marks forthe workstations in the machining line 22 do not have to be unique forthe entire machining line 22; the marks only have to be unique for aparticular zone (mark stamping area).

Based on the foregoing system, if the numbers 1, 2, 3 are present instamp marking area 254, an operator knows, inter alia, that thecrankshaft 250 was worked on by MC10 and MC3. If the numbers 1, 2, 3, 4are present in stamp marking area 256, the operator knows, inter alia,that the crankshaft 250 was worked on by MC13.

In addition to the stamp marking areas 252-264, the crankshaft containsalternate marking areas 270, 272, 274, 276 (shown in FIG. 11), withinwhich marks are made by marking devices other than stamping machines.Each of the alternate marking areas 270-274 represents a particularworkstation and the presence or absence of a mark in the area indicateswhether the workstation worked on the crankshaft 250. For example,alternate areas 270, 272, 274 may represent balance machines A, B, C,respectively, and the presence of a drill mark in alternate marking area272 informs an operator that balance machine B worked on the crankshaft250.

The marking system described above may be interpreted automatically byan identification apparatus, or may be interpreted by an operator. Ifthe marking system is interpreted by an operator, the operator may beprovided with an interpretation key in some form of a fixed medium, suchas diagrams on paper, similar to FIGS. 10 and 11, or in a computer filethat may be viewed on a computer display.

Preferably, a workpiece moving through the machining line 22 is markedat the drop-off station of each zone (by a stamping machine orotherwise) to indicate the workstation that worked on the workpiece inthe zone. Thus, for purposes of describing only a portion of themachining line 22, the crankshaft 250 is moved by the autoloader 10 fromthe input area 66 to the workstation MC2. The crankshaft 250 is workedon in workstation MC2 and is then moved by the autoloader 10 to thedrop-off station 68, where the crankshaft 250 is stamped by the stampingmachine 80 with a numeral 2 in position C of stamping area 254. Thecrankshaft 250 is then moved by the output conveyor 36 from the drop-offstation 68 to the second input area 70. The autoloader 32 moves thecrankshaft 250 from the second input area 70 to the workstation MC12,where the crankshaft 250 is worked on. The autoloader 32 then moves thecrankshaft 250 to the second drop-off station 74, where the crankshaft250 is stamped by a stamping machine (having substantially the sameconstruction and operation as the stamping machine 80) with a numeral 1in position B of stamping area 256. The crankshaft 250 is then moved bythe output conveyor 72 from the second drop-off station 74 to anotherzone, where the crankshaft 250 will be moved by another autoloader toanother workstation. This process continues until the crankshaft 250 isfinished.

The marking process described above will produce a workpiece having aplurality of markings that can be used by an operator to determine everyspecific workstation that worked on the workpiece. In this manner, if afinished workpiece exits the machining line 22 and is later found tohave a defect caused by a particular operation, the operator candetermine the specific workstation that caused the defect. As can beappreciated, this significantly helps maintain the quality of workpiecesbeing produced by the machining line 22.

While the invention has been shown and described with respect toparticular embodiments thereof, those embodiments are for the purpose ofillustration rather than limitation, and other variations andmodifications of the specific embodiments herein described will beapparent to those skilled in the art, all within the intended spirit andscope of the invention. Accordingly, the invention is not to be limitedin scope and effect to the specific embodiments herein described, nor inany other way that is inconsistent with the extent to which the progressin the art has been advanced by the invention.

1. A method of identifying work performed on a workpiece in a work linecomprising a plurality of zones, wherein each zone comprises a pluralityof workstations that perform the same type of operation, said methodcomprising the steps of: (a.) in a first one of the zones, moving theworkpiece from a first input area to a first workstation; (b.) workingon the workpiece in the first workstation; (c.) after step (b), movingthe workpiece to a first output area in the first one of the zones; (d.)marking the workpiece with a first mark at the first output area, saidfirst mark indicating that the first workstation worked on theworkpiece; (e.) moving the workpiece to a second input area in a secondone of the zones; (f.) moving the workpiece from the second input areato a second workstation in the second one of the zones; (g.) working onthe workpiece in the second workstation; (h.) after step (g.), movingthe workpiece to a second output area in the second one of the zones;and (i.) marking the workpiece with a second mark at the second outputarea, said second mark indicating that the second workstation worked onthe workpiece.
 2. The method of claim 1, further comprising the steps:(j.) moving the workpiece from the first workstation to a qualitycontrol station in the first one of the zones; and (k.) inspecting theworkpiece; wherein steps (j.) and (k.) are performed between steps (b.)and (c.); and wherein in step (c.), the workpiece is moved to the firstoutput area from the quality control station.
 3. The method of claim 1,wherein the first and second marks are in different locations on theworkpiece, and wherein the location of the first mark in combinationwith the nature of the first mark identifies the first workstation ashaving worked on the workpiece, and wherein the location of the secondmark in combination with the nature of the second mark identifies thesecond workstation as having worked on the workpiece.
 4. The method ofclaim 3, wherein the first and second marks are numeric characters. 5.The method of claim 4, wherein steps (d.) and (i.) are performed by apneumatic pin marking machine.
 6. The method of claim 4, wherein theworkpiece is an automotive crankshaft having first and secondcounterweights.
 7. The method of claim 6, wherein the location of thefirst mark is on the first counterweight and the location of the secondmark is on the second counterweight.
 8. The method of claim 7, whereinthe first and second counterweights are disposed at opposing ends of thecrankshaft.
 9. The method of claim 1, wherein steps (a.) and (c.) areperformed by a first autoloader, and wherein steps (f.) and (h.) areperformed by a second autoloader, and wherein each of the first andsecond autoloaders comprises a carriage movably mounted to a guidancestructure.
 10. A method of identifying workstations that performed workon a workpiece in a work line comprising a plurality of zones, whereineach zone comprises a plurality of workstations that perform the sametype of operation, said method comprising the steps of: (a.) providing aunique code for identifying each workstation; (b.) performing work onthe workpiece in one of the workstations in a first zone; (c.) markingthe workpiece in accordance with the code for the workstation thatworked on the workpiece in step (b.); (d.) performing work on theworkpiece in one of the workstations in a second zone; (e.) marking theworkpiece in accordance with the code for the workstation that worked onthe workpiece in step (d.); (f.) if there are zones following the secondzone, moving the workpiece to each of the following zones and performingwork on the workpiece in one of the workstations in each of thefollowing zones and marking the workpiece in accordance with the codefor the workstation that worked on the workpiece in each of thefollowing zones.
 11. The method of claim 10, wherein each of the uniquecodes comprises a mark and a location of the mark on the workpiece. 12.The method of claim 11, wherein the marks are on distinguishablydifferent components of the workpiece.
 13. The method of claim 11,wherein the unique codes comprise: first unique code types, wherein thelocation of the marks of said first unique code types are unique; andsecond unique code types, wherein the locations of the marks of thesecond unique code types are not unique.
 14. The method of claim 13,wherein the marks for the first code types are drill marks.
 15. Themethod of claim 13, wherein the marks for the second unique code typesare numeric characters.
 16. The method of claim 15, wherein the numericcharacters are single digit numerals.
 17. The method of claim 10,wherein the workpiece is an automotive crankshaft having first andsecond counterweights.
 18. The method of claim 17, wherein each of theunique codes comprises a mark and the location of the mark on theworkpiece; and wherein a portion of the locations of the unique codesare on the first counterweight and a portion of the locations of theunique codes are on the second counterweight.
 19. The method of claim18, wherein the first and second counterweights are disposed at opposingends of the crankshaft.
 20. The method of claim 10, wherein step (c.) isperformed by a pneumatic pin marking machine.
 21. The method of claim10, wherein steps (b.) and (c.) are performed for each of the zones inthe work line.
 22. The method of claim 21, wherein the workstations ineach zone perform a different operation than in the other zones.
 23. Amethod of identifying work performed on a workpiece in a work line saidmethod comprising the steps of: (a.) providing a first zone comprising afirst plurality of identical workstations that each perform a first typeof operation; (b.) in the first zone, moving the workpiece from a firstinput area to one of said first plurality of workstations; (c.) workingon the workpiece in the one of said first plurality of workstations;(d.) after step (c), moving the workpiece to a first output area in thefirst zone; (e.) marking the workpiece with a first mark at the firstoutput area, said first mark indicating which of said first plurality ofworkstations worked on the workpiece; (f.) providing a second zonecomprising a second plurality of identical workstations that eachperform a second type of operation; (g.) moving the workpiece to asecond input area in the second zone; (h.) moving the workpiece from thesecond input area to a one of said second plurality of workstations inthe second zone; (i.) working on the workpiece in the one of said secondplurality of workstations; (j.) after step (i.), moving the workpiece toa second output area in the second zone; and (k.) marking the workpiecewith a second mark at the second output area, said second markindicating which of the second plurality of workstations worked on theworkpiece.